We plan to study the turnover of membrane immunoglobulins in clones of human B lymphoblasts maintained in vitro, with particular regard to differences between IgM and IgD either in the unperturbed state or after exposure to anti-IgM or anti-IgD antibodies. Antigen-binding lymphoblastoid lines will also be prepared to study the effect of the antigen on the two classes of immunoglobulin receptors. We shall also study, with mouse lymphocytes, the regulation of immunoglobulin idiotypes, both for membrane and for secreted immunoglobulins in a system of polyclonal B cell activation (that is, an antigen-independent system). In such a system we shall also study the regulation of the "switch" from the synthesis of IgM to that of IgG, or, alternatively, to that of IgA. With the use of hybridomas producing antibodies against mouse IgG allotypes we are going to study the effect of IgD suppression in different immune responses in vivo or in vitro.